Transcript Chapter 3. QoS Mechanisms

Multimedia Wireless Networks:
Technologies,
Standards, and QoS
Chapter 3. QoS Mechanisms
TTM8100
Slides edited by Steinar Andresen
QoS Mechanisms
Traffic handling mechanisms
• (sometimes called In-traffic mechanisms)
are mechanisms that classify, handle,
police, and monitor the traffic across the
network. The main mechanisms are:
1. classification,
2. channel access,
3. packet scheduling, and
4. traffic policing.
Bandwidth management
mechanisms
• (sometimes called Out-of-traffic
mechanisms) are mechanisms that manage
the network resources (e.g., bandwidth) by
coordinating and configuring network
devices' (i.e., hosts, base stations, access
points) traffic handling mechanisms.
The main mechanisms are:
1. resource reservation signaling and
2. admission control.
Classification
Classification Techniques related
to OSI layers
OSI layer
Classification Techniques
Application
User/Application Identification
Transport
Flow (5 tuplet IP Address)
Network
IPTOS, DSCP
Data Link
802.1p/Q Classification
Physical Layer
Data Link Classification
(ref. 3- bits field IEEE 802 header)
Priority
0
1
2
3
4
5
6
7
Service
Default, assumed to be best
effort service
Less than best effort service
Reserved
Reserved
Delay sensitive, no bound
Delay sensitive, 100ms bound
Delay sensitive, 10ms bound
Network control
Network Layer Classification
Network layer, or Layer 3 classification is using
Layer 3 header.s Layer 3 classification enables
service differentiation in Layer 3 network.
• An example of Layer 3 classification is IPTOS (Internet
protocol type of service
– IPv4 and IPv6 standard defined a prioritization field in the IP
header RFC 1349 defined a TOS field in IPv4 header. The type
of service field consists of a 3-bit precedence subfield, a 4-bit
TOS subfield, and the final bit which is unused and is set to be 0.
The 4-bit TOS subfield enables 16 classes of service. In IPv6
header there is an 8-bit class of service field
• and DSCP (Internet protocol differential service code point).
– Later IETF’s differentiated services working group redefined
IPv4 IPTOS to be DSCP,. DSCP has a 6-bit field enabling 64
classes of service.
Structure of IPTOS and DSCP in IPv4
2-bit
Unused
6-bit DSCP
0
0
DSCP
7
3-bit
Precedence
4-bit
4-bit
version header l
4-bit TOS
IPTOS
16-bit total length (in bytes)
8-bit TOS
16-bit identification
8-bit TTL
0
8-bit Protocol
3-bit
13-bit fragment offset
flag
16-bit header checksum
32-bit source IP address
32-bit destination IP address
DATA
31
Structure of IPTOS and DSCP in IPv6
0
4-bit
version
31
8-bit traffic
class
Payload Length
Flow Label
Next Header
Payload Length
Payload length
Hop Limit
Transport Layer Classification
A 5-tuplet IP header
• source IP,
• destination IP,
• source port,
• destination port, and
• protocol IP)
can be used for transport layer classification.
Transport Layer Classification
A 5-tuplet IP header can uniquely identify the
individual application or flow. This classification
provides the finest granularity and supports perflow QoS service.
Limitations:
• OK at the EDGE, but NOT Suitable to CORE
• Problems when passing firewalls using NAT
Application or User Classfication
The users or applications can be uniquely
identified by an ID and a central agency in
the network can be made responsible to
– allow or reject
requests for new sessions, depending on
the traffic situation. Normally each session
also will be given a unique ID number.
Channel Access Mechanisms
There is two options to channel access control:
1. Collision based access and
2. Collision-free channel access
•
Collision based access needs a MAC protocol
that tries to avoid and resolve collisions (in the
case they occur). E.g. CSMA/CD. Service level
can be improved by:
– Over-provisioning or
– Adding a priority scheme
Collision-Free Channel Access
• Polling
• TDMA - illustrated here -static or dynamic
Packet Scheduling Mechanisms
- Hierarchical
or
- Flat Packet scheduling
FIFO Packet Scheduling
Strict Priority Packet Scheduling
Weight Fair Queue (WFQ)
Traffic Policing Mechanisms
(A):
Incoming traffic with rate R
which is less than the bucket rate r.
The outgoing traffic rate is equal to R.
In this case when we start with an
empty bucket, the burstiness of
the incoming traffic is the same as
the burstiness of the outgoing traffic
as long as R < r.
Traffic Policing Mechanisms
(B):
Incoming traffic with rate R
which is greater than the bucket rate r.
The outgoing traffic rate is equal to
r (bucket rate).
Traffic Policing Mechanisms
(C):
Same as (B) but the bucket is full.
Non-conformant traffic is either
dropped or sent as best effort traffic.
Token Bucket Mechanism (A)
The incoming traffic rate is less than the token
arrival rate. In this case the outgoing traffic
rate is equal to the incoming traffic rate.
Token Bucket Mechanism (B)
The incoming traffic rate is greater than the
token arrival rate. In case there are still tokens
in the bucket, the outgoing traffic rate is equal
to the incoming traffic rate.
Token Bucket Mechanism (C)
If the incoming traffic rate is still greater than the token arrival
rate (e.g., long traffic burst), eventually all the tokens will be
exhausted. In this case the incoming traffic has to wait for the
new tokens to arrive in order to be able to send out. Therefore,
the outgoing traffic is limited at the token arrival rate.
Resource Reservation Signaling
Mechanisms
• Provision of resource reservation signaling that
notifies all devices along the communication path
on the multimedia applications' QoS requirements.
• Delivery of QoS requirements to the admission
control mechanism that decides if there are
available resources to meet the new request QoS
requirements.
• Notification of the application regarding the
admission result.
Resource Reservation Signaling
Mechanisms
Admission Control
– Explicit admission control:
This approach is based on explicit resource reservation.
Applications will send the request to join the network through
the resource reservation signaling mechanism. The request that
contains QoS parameters is forwarded to the admission control
mechanism. The admission control mechanism decides to accept
or reject the application based on the application's QoS
requirements, available resources, performance criteria, and
network policy.
– Implicit admission control:
There is no explicit resource reservation signaling. The
admission control mechanism relies on bandwidth overprovisioning and traffic control (i.e., traffic policing).
QoS Architecture
• Applications with quantitative QoS requirements: mostly
require QoS guaranteed services. Therefore, explicit
resource reservation and admission control are needed, also
require strict traffic control (traffic policing, packet
scheduling, and channel access).
• Applications with qualitative QoS requirements: require
high QoS levels but do not provide quantitative QoS
requirements. We can use resource reservation and
admission control. They also require traffic handling which
delivers differentiated services.
• Best effort: There is no need for QoS guarantees. The
network should reserve bandwidth for such services. The
amount of reserved bandwidth for best effort traffic is
determined by the network policy.
QoS Architecture for Infrastructure
based Wireless Networks
QoS Architecture for Ad Hoc Wireless
Networks